A spectrum analyzer is essentially a receiver that is tuned or swept across a band of frequencies, and the amplitude of received signals is displayed on a cathode ray tube as a function of frequency. It is often desirable to make adjustments to the displayed signal information for the purposes of calibration, and it is also desirable to quantify the characteristics of the displayed information such as signal magnitude and frequency. These functions are most effectively performed if the information is converted from analog form to digital form and stored in a memory. Such digitization of the information also facilitates the automation of spectrum analyzer functions.
An automatic spectrum analyzer is disclosed in U.S. Pat. Nos. 4,253,152; 4,264,958; 4,257,104; and 4,244,024 which has a number of advanced data handling and analysis features, several of them connected with markers that can be placed on the display screen. These features allow the user to determine, for example, the frequency and amplitude of a particular point on a signal trace in the display where he has placed a marker. The user can also request the marker to be placed at the highest signal shown in the display with a peak search function, and the display will show the frequency and amplitude of the point found by the search. Another prior art spectrum analyzer, the Hewlett-Packard model 8566A, had an additional feature that allowed the user to have a marker placed on the next highest peak.
Another feature of the prior art device allows the user to specify a particular frequency on the display and then to cause a marker to be placed on the signal trace in the display at that frequency. The spectrum analyzer will then display the amplitude of the signal at the chosen frequency.
The prior art spectrum analyzer can be controlled from a keyboard on the front panel of the instrument or from a remote computer connected to the analyzer by the Hewlett-Packard Interface Bus (HP-IB). Using commands that represent functions available from the front panel of the instrument, a remote computer can thus programmatically control the spectrum analyzer.